The Cowes RNLI Lifeboat was launched this morning to assist a vessel sinking in the Solent with 15 people on board.
As the crew sat on board ready to launch, VHF radio broadcasts suggested the Mayday alert may have been called in error.
HM Coastguard required Cowes RNLI crews to launch as a precaution but cancelled the launch soon after the lifeboat had left Cowes.
The Coastguard confirmed with the vessel that the MAYDAY was a training exercise.
Ryde Inshore Lifeboat and the Coastguard Rescue Helicopter were also alerted.